Inchworm® motor systems are used in many application to precisely position components of mechanical and optical systems. One application is for precisely positioning reflective mirrors of telescopes deployed by satellites and another for ® positioning mirrors or lenses in terrestrial telescopes. For example, a typical satellite telescope system may comprises multiple mirrors that are folded at launch and are deployed in outer space. It is critical that the deployed mirrors be finely adjusted to precise location along the optical axis of the telescope. Inchworm® motor control systems can precisely position the mirrors to within nanometers of a desired position. Such Inchworm® motors may also compensate for atmospheric affects on terrestrial telescopes. The Inchworm® motor may be coupled to an atmospheric sensing system that detects perturbations produced by the atmosphere. The Inchworm® motor will operate as part of a high speed closed loop control system to make nanometeric adjustments to the telescope's mirrors and thereby correct the apparent atmospheric perturbations
The problem encountered is to design a system with tight tolerances that needs little alignment after deploying (attempting to mimic a monolithic system) or a system utilizing a positioning system that accommodates a wide range of adjustment with nanometer control resolution. The positioning needs are several. First, after deployment, the optical elements need to be positioned relative to each other in the range of the wavelengths of interest. If an optical element is segmented, each segment needs to be at the same phase of the wavefront. Second, while in operation there will be thermal excursions of the whole system or of some parts of the system. This will cause differential movement of the optical elements. Third, the articulated low mass optical elements will be considerably less stiff than a monolithic design. This will cause differential movement as a function of force applied to and the stiffness of the particular load path. The forces will change as a function of movement for targeting. Fourth, dynamic correction of the optical elements (adaptive optics) for atmospheric or other perturbations is a lower travel range but higher frequency need.
Another application area is large laser-based systems. The large optical elements need alignment in the 10-nm range with forces exceeding 100 N3. As before, designs can go to elaborate lengths to isolate system movements or they can accommodate the inevitable changes with active position control. To date, the alignment systems utilize a serial approach with one technology for coarse adjustment and a different technology for precision adjustment. While land-based systems can accommodate the larger volume and mass of dual positioning systems, this approach does impact overall system size. Secondly, dual-positioning systems require another level of control software to manage and trade-off control between the systems. A single actuator with stiffness of 25 N/μm probably exceeds any serial design capability. Conceivably having the capability to remotely compensate for 10+ millimeters of change would lessen sub-system tolerances, setup procedure complexity, operational downtime and subsequent costs.
Inchworm® motors and their control systems are prime candidates for achieving the gross and fine positioning requirements in a single motor system. However, prior motor drives rely upon conventional Class A linear amplifiers to provide the energy for operating the motors. Inchworm® motors typically translate a load forward or reverse along a given path. Conventional motor drives contain linear amplifiers to power the motor. The Inchworm® motor is mostly a capacitive load. As such, it must be charged to move in one direction and discharged to move in the other direction.
Linear power supplies are notoriously inefficient. They typically include Class A amplifiers that consume power whenever they are turned on even if the motor is quiescent. They have other drawbacks, including a large number of components and relatively high power consumption. Since low mass and low power consumption are primary considerations for satellite components, those skilled in the art are looking for a more efficient amplifier that has few components and less mass.
One attractive candidate is switching power amplifiers also known as class D amplifiers. These components are more efficient than a typical Class A circuit. Some achieve efficiencies at or above 90%. However, a typical boost or buck converter has other problems. For one, the operating frequency is normally quite high if one has to avoid interference with the switching frequency. Also, a typical boost or buck converter has relatively large ripple currents that detract from the precise voltage supply needed to operate the sensitive Inchworm® motors. As such, there is an unmet need for an efficient, low mass power amplifier that can operate Inchworm® motors.